The present invention relates to apparatus, system, and method for cryoablating tissues of a body. More particularly, the present invention relates to a heatable and coolable cryoprobe having an operating tip, which tip is operable to be cooled by rapid decompression of a high-pressure cooling gas expanding through a Joule-Thomson orifice, and also operable to be heated by a flow of electrically heated low-pressure cooling gas transiting that Joule-Thomson orifice.
In recent years, cryoablation of tissues has become an increasingly popular method of treatment for a variety of pathological conditions. Malignancies in body organs such as the breast, prostate, kidney, liver, and other organs are successfully treated by cryoablation, and a variety of non-malignant pathological conditions, such as benign prostate hyperplasia, benign breast-tumors, and similar growths are also well treated by cryoablation of unwanted tissues. Certain cases of intractable chronic pain are also treatable through cryosurgery, by cryoablation of selected nervous tissue.
Cryoablation of pathological tissues or other unwanted tissues is typically accomplished by utilizing imaging modalities, such as x-ray, ultrasound, CT, and MRI, to identify a locus for ablative treatment, then inserting one or more cryoprobes into that selected treatment locus, then cooling the treatment heads of the inserted cryoprobes sufficiently to cause the tissues surrounding the treatment heads to reach cryoablation temperatures, typically below about −40° C.
Tissues thus cooled are thereby caused to loose their functional and structural integrity. Cancerous cells cease growing and multiplying, and cryoablated tumor tissue materials, whether from malignant tumors or from benign growths, lose their structural integrity and are subsequently sloughed off or absorbed by the body.
One well-known technical problem in cryoablation is that when a cryoprobe is introduced into an organ or other body part and cooled to cryoablation temperatures, tissues contiguous to the cryoprobe immediately adhere to the probe, sticking to the probe as an ice cube adheres to the hand of an unwary householder using wet fingers to pick up an ice cube from his deep freeze.
Adherence of body tissues to a cryoprobe cooled to cryoablation temperatures has the effect of immobilizing that probe, which remains fixed in place until those contiguous tissues thaw and cease to adhere to the probe. Attempts to move or remove a probe by force, while body tissues adhere to the probe, risks tearing or otherwise damaging those tissues.
Adherence of tissues to operating cryoprobes is known to be a source of considerable delays in cryoablation surgery. Such delays are particularly problematic under currently preferred cryosurgery methods, which call for freezing, thawing, and refreezing of tissues, and which may utilize a given probe sequentially in a plurality of positions within an organ, during a process by which a cryoablation locus is shaped and ‘sculpted’ so as to encompass and destroy a lesion of known three-dimensional shape.
Consequently, currently preferred cryosurgery practice utilizes a cryoprobe which is heatable as well as coolable, thereby enabling to cool a cryoprobe to cryoablation temperatures, thereby cooling tissues surrounding that probe to cryoablation temperatures, and then to heat the probe sufficiently to thaw tissues touching the probe, thereby releasing adhesions between probe and tissue and enabling a surgeon to remove the probe, or reposition it.
Thaw heating is most typically used to free the cryoprobe from adhesion to the tissue after cryoablation, permitting rapid removal of a cryoprobe from an ablation site, thereby increasing the efficiency of, and shortening time required for, medical procedures. Thaw heating is particularly useful when it is desired to rapidly repositioning a cryoprobe for sequential use at a plurality of sites.
Certain cryoablation procedures require thaw heating as a safety precaution. In cryosurgical treatment of epicardial arrhythmia, for example, thawing may be used to protect sensitive tissues from tearing or other damage which might otherwise be caused when delicate tissues adhere to a cryoprobe held in the hands of a surgeon, where any slight unintentional movement by the surgeon risks tearing those delicate adhering tissues.
Heating is also used as a part of cryoablation procedure itself. It has been found that cycles of freezing, thawing, and re-freezing are more efficiently destructive of cell structure than is the process of freezing alone.
It is also convenient to have a cryoprobe which can be independently either heated or cooled: such multi-function probes can be used in collective probe configurations to selectively cool and ablate an ablation target using selected cooling probes, while utilizing other selected probes (possibly of identical construction, but used in heating mode) to heat other tissues which a surgeon desires to protect.
Of known heatable and coolable cryoprobe systems, the currently preferred systems utilize a dual gas supply module. Dual gas supply modules comprise a source of high-pressure cooling gas, such as argon, and a source of high-pressure heating gas, such as helium. As will be explained in further detail hereinbelow, high-pressure cooling gas, such as argon, when allowed to expand through a small (Joule-Thomson) orifice into an expansion chamber and thereby rapidly expand to a lower pressure, becomes extremely cold. Gas cooled in this manner can be used to cool the operating tip of a cryoprobe. In contrast, a high-pressure heating gas, such as helium, when allowed to expand through such an orifice becomes hotter. Gas heated in this manner is typically used to heat contemporary Joule-Thomson cryoprobes. The technology involved is set forth in U.S. Pat. No. 5,522,870 and U.S. Pat. No. 5,702,435, both entitled “Fast-changing heating-cooling device and method, to Ben-Zion Maytal.
A major advantage of Maytal's system is that the heating apparatus and the cooling apparatus of the cryoprobe are the same: a single gas input lumen, heat exchanging configuration, Joule-Thomson orifice, expansion chamber and gas output lumen can serve to cool, when a high-pressure cooling gas is supplied, and to heat, when a high-pressure heating gas is supplied. A system utilizing such a probe need only be operable to supply either a cooling gas or a heating gas, at the direction of a surgeon, as needed.
Such systems typically comprise two high pressure gas supply tanks, and sequences of one-way valves and gas control valves operable, manually or under remote control, to stop and start flows of heating or cooling gasses, as commanded by a surgeon or by a computerized command module.
Such systems, however, present a disadvantage. A dual gas supply includes two gas tanks, typically large and heavy, and a complex setup of valves and servomotors to control output from the dual gas supply, all made necessary by the need to supply two different kinds of gas, during different phases of a same surgical procedure, to a same Joule-Thomson heater/cooler.
Thus there is a widely recognized need for, and it would be highly advantageous to have, an apparatus and method providing the capabilities and advantages of fast heating and fast cooling of a cryoprobe, yet which does not require a dual gas supply system.
Prior art cryoprobes have used various additional means for heating cryprobe operating tips to facilitate disengagement of cryoprobes from frozen tissue.
U.S. Pat. No. 3,913,581 to Ritson et al. teaches configurations operable to cool an operating tip of a cryoprobe by decompressive expansion of a high-pressure gas through a Joule-Thomson orifice into an expansion chamber, and further operable to heat that operating tip by rapidly introducing high-pressure gas into that expansion chamber through a high-volume entrance to the chamber, rather than through a Joule-Thomson orifice, so that the introduced gas does not expand (decompress), but remains at, or rapidly returns to, high pressure. Riston teaches that rapid re-pressurization of the expansion chamber has the effect of causing a cooling fluid supplied as a gas to condense on cold portions of the probe thereby heating those portions.
A disadvantage of Ritson's configuration is that it fails to provide rapid and effective and sufficient heating. A further disadvantage is that Ritson's configuration requires a high-pressure valve on a high-pressure gas input line, used to switch high-pressure gas from a first gas input line (for conducting high-pressure input gas to the Joule-Thomson orifice, in cooling phase) to a second gas input line, which second line is in non-restricted fluid communication with the expansion chamber. (Ritson's second gas input line also serves as a gas exhaust line during cooling phases of operation.)
Providing the required valve inside the probe and within or near the operating tip is difficult, particularly in view of the extreme miniaturization of cryoprobes in preferred use today. Manipulating such a valve during a surgical procedure is difficult also. Providing the required valve outside the probe, on proximal portions of the gas input lines, creates a latency which causes a lagging response time when switching between heating phase and cooling phase of operation. Further, Riston's configuration calls for two gas input lumens in the cryoprobe, both strong enough to safely withstand high-pressured gas. This requirement also creates a barrier to extreme miniaturization of cryoprobes.
U.S. Pat. No. 5,338,415 to Glinka also teaches a cryoprobe having a variable gas passageway enabling gas from a gas supply line within a cryoprobe to bypass a Joule-Thomson orifice in the probe and to exhaust directly from the probe without significant decompression. In Glinka's configuration, a valve is provided for enabling most of a high-pressure input gas to rapidly traverses a gas input line and pass into a second gas exhaust path. Glinka teaches that mass flow of a high-pressure room-temperature gas which traverses most of the body of a probe without significant expansion therein is operable to heat portions of the probe. (In Glinka's configuration, most of the traversing high-pressure gas does not penetrate into the probe's expansion chamber.) Glinka's configuration is primarily used for cleaning a probe's gas supply line after cooling, but Glinka notes that continuous rapid movement of high-pressure gas through the probe will serve eventually to bring a cold probe back to room temperature.
A disadvantage of Glinka's configuration is that it too fails to provide rapid and effective and sufficient heating. A further disadvantage of Glinka's configuration is that it also requires an additional gas lumen within the body of the probe, which lumen must, like the gas input lumen common to all Joule-Thomson cryoprobes, be constructed to withstand gas input pressures which may be as high as 4000-6000 psi. The requirement for this additional high-pressure lumen is problematic in the context of the highly miniaturized cryoprobes in preferred use today.
Longsworth, in U.S. Pat. No. 5,452,582, provides yet another configuration for gas heating of a Joule-Thomson cooled cryoprobe. Longsworth's configuration provides a first gas supply line for high-pressure cooling gas, and a second gas input line into the probe for a room-temperature warming gas supplied at about 100 psi. Cooling gas supplied at high pressure through Longsworth's first gas supply line flows through a Joule-Thomson orifice to provide Joule-Thomson cooling of an operating tip of the probe. Room temperature gas supplied through Longsworth's configuration does not pass through a Joule-Thomson orifice. Passage of this room-temperature gas, bypassing the Joule-Thomson orifice, is used to heat the probe.
A disadvantage of Longsworth's configuration is that it too requires an additional gas input lumen extending into a distal portion of the cryoprobe. A probe requiring this second gas input lumen is disadvantageous in construction of a highly miniaturized cryoprobes in preferred use today.
Thus, there is a widely recognized need for, and it would be highly advantageous to have, a cryoprobe configuration which enables heating of a cryoprobe operating tip by low-pressure flow of gas, yet which does not require a plurality of gas input lines into the cryoprobe, does not require a plurality of gas inputs into an expansion chamber of that operating tip, and does not require a plurality of gas exhaust lines from that operating tip.
Further, there is a widely recognized need for, and it would be highly advantageous to have, a cryoprobe configuration which enables heating of a cryoprobe operating tip by flow of cooling gas through the probe, yet which does not require a switchable gas flow nozzle within the probe, and does provide for rapid switching from cooling to heating modes of operation.
Rabin, in U.S. Pat. No. 5,899,897 entitled “Method and apparatus for heating during cryosurgery” presents a cryoheater heated by electrical resistance heating. Rabin teaches that his cryoheater may be used in conjunction with one or more cooling cryoprobes to protect tissues in proximity to a cryoablation site. Rabin does not, however, disclose a probe operable both to heat and to cool.
Electrical heating of the external operating surfaces of a cryoprobe is not a trivial endeavor. Electrically heated surfaces must necessarily be electrically isolated from body tissues, least electric current leak into the tissues. Consequently, the probe surface in contact with body tissues cannot itself be an electrical resistance element. To heat a probe's external surface electrically, one must heat a resistance element inside the probe, and then rely on an intermediate substance to transfer heat to the external surface.
Such a process presents several problems. A heating element within an operating tip of a cryoprobe cannot be placed in direct contact with an outer (typically metallic) wall of that operating tip, since an electrical isolating layer is required to prevent current leakage from the resistance element into the tip wall and thence into body tissues. Electrical resistance elements, of course, are poor conductors of electricity, since it is the power expended across the internal resistance of such heating elements which causes the heating process. However, poor conductors of electricity are typically also poor conductors of heat. Consequently, an electrical resistance element placed in immediate proximity to an external heat-conducting wall of an operating tip of a cryoprobe will inevitably at least partially interfere with the process by which that wall is cooled, during cooling phases of utilization of the cryoprobe.
Thus, a configuration which places an electrical resistance element, and it's necessary electrical insulating layer, within or immediately contiguous to an exterior wall of a probe would enabling heating of that probe, but would also inevitably interfere with the cryoprobe cooling process. Joule-Thomson cooling takes place when a high-pressure cooling gas expands through a Joule-Thomson orifice into an expansion chamber. The expanded gas is thereby cooled to very cold temperatures. When exterior walls of that expansion chamber are also the outer walls of the cryoprobe operating tip, and those outer walls of the cryoprobe operating tip are made of a thermally conductive material, then the cold gas within the probe tip rapidly and efficiently cools the highly heat-conductive operating tip wall, which in turn rapidly and efficiently cools the surrounding tissue to cryoablation temperatures. If, however, an electrical resistance element and its necessary electrical insulation layer are interposed between the expansion chamber volume and the walls defining that volume, as would be the case if electrical resistance elements are placed within, contiguous to, or indirect contact with, those walls, then both the resistance elements themselves and their required electrically isolating layer will interfere with heat transfer between the heat-conductive outer walls and the cold gas contained in the expansion chamber volume, during cooling operation of the probe, since by their nature, electrical insulators and electrical resistance materials are poor conductors of heat.
Thus, electrical resistance elements and electrical insulating layers in proximity to external walls of the operating tip of a probe (or, alternatively, positioned within those walls) would significantly interfere with the Joule-Thomson cooling process, as described.
Consequently, there is a widely recognized need for, and it would be highly advantageous to have, a system for electrical resistance heating of a cryoprobe which does not interfere with the probe's Joule-Thomson (or other) cooling processes.